The fuel inside the fuel tank is transferred to an internal combustion side through a suction pipe disposed inside the fuel tank and the like. In order to remove water from the fuel transferred in this manner and also prevent dust from being sent to a fuel pump, a filter device is attached to the fuel suction port and the like of such suction pipe. As such filter device, there is a filter device shown in Patent Document 1 disclosed by the present applicant.
The filter device of the Patent Document 1 includes a bag-like filter body allowing an internal space to communicate with the fuel suction port located inside the fuel tank. Such filter body includes two layers of a filter material made of a non-woven fabric formed by a melt-blown method between the filter material of the outermost layer made of a woven mesh and the filter material of the innermost layer made of a non-woven fabric formed by a spunbond method. Then, the average diameter of the pores of the non-woven fabric formed by the melt-blown method located on the inner side is made smaller than the average diameter of the pores of the non-woven fabric formed by the melt-blown method located on the outer side, and a filtration gradient (also called a filtration accuracy gradient and the like) is provided in the filter body. Thereby, while allowing fine dust to be trapped, by reducing the load on the filter material made of the non-woven fabric formed by the melt-blown method located on the inner side where the average diameter of the pores is small, a long-life filter device can be provided.
In the filter device constituted in this manner, the filtration gradient is made gentle by overlaying further more filter materials made of the non-woven fabric formed by the melt-blown method whose average diameter of the pores differs (the difference of the average diameter of the pores of adjacent filter materials is reduced). While improving filtration accuracy, a long-life filter device can be provided. However, given the manufacturing cost of the filter body, the overlaid number of the filter materials is limited. Also, the more the overlaid number of the filter materials, the number of the filter materials increases at a welded portion which is carried out in order to be bag-like, so that due to such welding, it is difficult to constitute the filter body appropriately.